1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/mfbt/Compression.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,116 @@
1.4 +/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.6 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.7 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.8 +
1.9 +/* Various simple compression/decompression functions. */
1.10 +
1.11 +#ifndef mozilla_Compression_h_
1.12 +#define mozilla_Compression_h_
1.13 +
1.14 +#include "mozilla/Types.h"
1.15 +#include "mozilla/Assertions.h"
1.16 +
1.17 +namespace mozilla {
1.18 +namespace Compression {
1.19 +
1.20 +/**
1.21 + * LZ4 is a very fast byte-wise compression algorithm.
1.22 + *
1.23 + * Compared to Google's Snappy it is faster to compress and decompress and
1.24 + * generally produces output of about the same size.
1.25 + *
1.26 + * Compared to zlib it compresses at about 10x the speed, decompresses at about
1.27 + * 4x the speed and produces output of about 1.5x the size.
1.28 + *
1.29 + */
1.30 +
1.31 +class LZ4
1.32 +{
1.33 +
1.34 +public:
1.35 +
1.36 + /**
1.37 + * Compresses 'inputSize' bytes from 'source' into 'dest'.
1.38 + * Destination buffer must be already allocated,
1.39 + * and must be sized to handle worst cases situations (input data not compressible)
1.40 + * Worst case size evaluation is provided by function maxCompressedSize()
1.41 + *
1.42 + * @param inputSize is the input size. Max supported value is ~1.9GB
1.43 + * @param return the number of bytes written in buffer dest
1.44 + */
1.45 + static MFBT_API size_t compress(const char* source, size_t inputSize, char* dest);
1.46 +
1.47 + /**
1.48 + * Compress 'inputSize' bytes from 'source' into an output buffer
1.49 + * 'dest' of maximum size 'maxOutputSize'. If it cannot achieve it,
1.50 + * compression will stop, and result of the function will be zero,
1.51 + * 'dest' will still be written to, but since the number of input
1.52 + * bytes consumed is not returned the result is not usable.
1.53 + *
1.54 + * This function never writes outside of provided output buffer.
1.55 + *
1.56 + * @param inputSize is the input size. Max supported value is ~1.9GB
1.57 + * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
1.58 + * @return the number of bytes written in buffer 'dest'
1.59 + or 0 if the compression fails
1.60 + */
1.61 + static MFBT_API size_t compressLimitedOutput(const char* source, size_t inputSize, char* dest,
1.62 + size_t maxOutputSize);
1.63 +
1.64 + /**
1.65 + * If the source stream is malformed, the function will stop decoding
1.66 + * and return a negative result, indicating the byte position of the
1.67 + * faulty instruction
1.68 + *
1.69 + * This function never writes outside of provided buffers, and never
1.70 + * modifies input buffer.
1.71 + *
1.72 + * note : destination buffer must be already allocated.
1.73 + * its size must be a minimum of 'outputSize' bytes.
1.74 + * @param outputSize is the output size, therefore the original size
1.75 + * @return the number of bytes read in the source buffer
1.76 + */
1.77 + static MFBT_API bool decompress(const char* source, char* dest, size_t outputSize);
1.78 +
1.79 + /**
1.80 + * If the source stream is malformed, the function will stop decoding
1.81 + * and return false.
1.82 + *
1.83 + * This function never writes beyond dest + maxOutputSize, and is
1.84 + * therefore protected against malicious data packets.
1.85 + *
1.86 + * note : Destination buffer must be already allocated.
1.87 + * This version is slightly slower than the decompress
1.88 + * without the maxOutputSize
1.89 + *
1.90 + * @param inputSize is the length of the input compressed data
1.91 + * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
1.92 + * @param outputSize the actual number of bytes decoded in the destination buffer (necessarily <= maxOutputSize)
1.93 +
1.94 + */
1.95 + static MFBT_API bool decompress(const char* source, size_t inputSize, char* dest,
1.96 + size_t maxOutputSize, size_t *outputSize);
1.97 +
1.98 + /*
1.99 + Provides the maximum size that LZ4 may output in a "worst case"
1.100 + scenario (input data not compressible) primarily useful for memory
1.101 + allocation of output buffer.
1.102 + note : this function is limited by "int" range (2^31-1)
1.103 +
1.104 + @param inputSize is the input size. Max supported value is ~1.9GB
1.105 + @return maximum output size in a "worst case" scenario
1.106 + */
1.107 + static inline size_t maxCompressedSize(size_t inputSize)
1.108 + {
1.109 + size_t max = ((inputSize) + ((inputSize)/255) + 16);
1.110 + MOZ_ASSERT(max > inputSize);
1.111 + return max;
1.112 + }
1.113 +
1.114 +};
1.115 +
1.116 +} /* namespace Compression */
1.117 +} /* namespace mozilla */
1.118 +
1.119 +#endif /* mozilla_Compression_h_ */
